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Compound Parallelogram Four-bar Linkage - Patent 4567782

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Standard four-bar parallelogram linkages are widely used. These devices have limited angular range capacity and their stiffness varies with angle. In such linkages, the links will deform in use. This deformation introduces linkage resonanceswhich is a disadvantage when using such linkages in high performance servo control loops.Also, conventional four-bar parallelogram linkages are limited in use to less than ninety degrees rotation because at the ninety degree point they can invert and lose their proper angular orientation. This is a serious problem in controlmechanism,s particularly in an arrangement such as a high performance servo control loop.A solution to these problems has been sought which would provide a linkage with large angle capability and with constant stiffness.SUMMARY OF THE INVENTIONThe disadvantages of the prior art are overcome by the device of the present invention which includes a first primary pivotal link means wherein the pivot points form a ninety degree angle, a second primary pivotal link means wherein the pivotpoints form a ninety degree angle, and connector means which connects the first primary link means with the second primary link means, whereby rotation of one primary link means creates rotation of the other primary link means without varying theresonant frequency range, and the stiffness of the linkage is independent of its angle of rotation. DESCRIPTION OF THE DRAWINGSFIG. 1 is a side elevation view of the parallelogram linkage of the present invention.FIG. 2 is a diagram which illustrates the linkage of FIG. 1 schematically.FIG. 3 is a diagram illustrating the loading of the linkage shown in FIG. 1.FIG. 4 is a block diagram of a typical electromechanical servo loop.FIG. 5 is a graph of the bode response of the servo loop shown in FIG. 4.FIG. 6 is a side elevation view showing a conventional four-bar linkage which is commonly used.FIG. 7 is a schematic diagram representing the linkage of FIG. 6.FIG. 8 is a schematic diagram il

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